Field of the Invention
The present invention relates to detectors of fluid flow effects and, more particularly, to detectors for measuring the mass flow in a flow of gas or the separated constituents in a gas flow.
Fluid flow effects detectors are necessary in many process control situations and in many instrumentation situations. They are used for measuring gas flow in such situations as monitoring heating, ventilation and air conditioning systems, engine intake flows, gas chromatography eluted gas flows, etc.
There are several kinds of detectors used for measuring various aspects of fluid flows. In measuring mass flow rates, for instance, a hotwire anemometer operates by having a heated wire placed across the fluid flow so that the extent of the cooling effect of the fluid on the wire can be measured. Alternatively, a thermistor can be placed in the flowing fluid for this purpose. More recently, various integrated circuit device arrangements supporting a metalization structure in or adjacent the flowing fluid have been used for such measurements to reduce detector size thereby improving sensitivity and, because of batch fabrication techniques, to also reduce detector cost.
There is a need in many mass flow measurement situations for detectors that have a very small thermal mass to reduce the time constants in the detector response to changes in gas flow conditions thereabout. Further, many gas flow situations such as in gas chromatographs have gas flowing in quite small dimension passageways. Thus, a detector structure should correspondingly be adapted for use with such geometrical arrangements.